1. Field of the Invention
This invention relates to a control device for an engine of an automobile for controlling the engine of an automobile wherein, when a power source relay for supplying power to the device per se, is switched to OFF, in compliance with an outside switch, a delay control is performed through a program for performing initializing operations of actuators.
2. Discussion of Backgroud
Among various functions of the control device for an engine of an automobile, there are initializing operations of actuators installed in various positions of an engine. Generally, this initializing operation is performed for the purpose of detecting a reference position of an actuator or checking the operation thereof. The operation is performed during non-operation of an engine instantly after power supply is ON, or instantly before power supply is OFF, so that it does not interfere with a normal control operation.
As an example of the initializing operation, a device is known wherein an idling revolution speed of an engine is controlled by controlling air quantity bypassing a throttle valve as shown in FIG. 3. This is called an ISC device, and the construction thereof is as shown in FIG. 3.
In FIG. 3, a reference numeral 11 designates an engine, 15, a throttle valve which moves cooperating with an accelerator and controls an intake quantity of air to the engine 11, 12, an idling switch showing that the throttle valve 15 is fully closed when a driver steps off the accelerator, and the engine 11 is in an idling state, and 16, a sensor for detecting an engine speed.
A numeral 14 designates an ISC device which receives signals from the idling switch 12 and the engine speed sensor 16, and controls an air quantity in a throttle valve bypass passage by operating an ISC (idling speed control) actuator 13, for controlling the engine speed to a predetermined value when the engine 11 is in the idling state.
As shown in FIG. 4, the air quantity passing through the bypass passage, is obtained by detecting an operational position of the ISC actuator 13 (position of an end portion 17 of the ISC actuator). In FIG. 4, the bold line shows a fully open position of an actuator, and the broken line, a fully closed position thereof.
On the other hand, the operational position of the ISC actuator 13 is detected as a relative position from the fully closed or the fully open position of the ISC actuator 13. Accordingly, it is necessary to always recognize the reference position (the fully closed position or the fully open position) of the ISC actuator 13. This is performed by operating the ISC actuator 13 until it reaches a maximum movable position (the fully closed position or the fully open position) as an initializing operation.
In this way, the ISC device 14 always detects the operational position of the ISC actuator 13, is capable of detecting the air quantity flowing in the bypass passage, and capable of controlling the ISC actuator 13 at a predetermined position (an ISC actuator position for flowing air in the bypass passage which corresponds to a required air quantity on the engine side) during off-idling operation, thereby enabling a smooth switching of the engine to the idling operation, thereafter.
When the initializing operation is performed instantly after the power is ON, in case that the engine is started up instantly after the power is ON, it may be necessary to start a principal control during the initializing operation.
Furthermore, when the initializing operation is performed instantly before the power is OFF, and when the initializing operation is performed at a timing when the power supply is switched to OFF, the actuator stops operating at that time point. Accordingly, since the detection of the actuator position can not be performed when the power supply is ON in the next operation, the control behavior thereafter may be malfunctioned.
Therefore, to prevent this, it becomes necessary to switch the power supply to OFF with certainty after the initializing operation is finished.
To realize this, a construction may be considered wherein the power supply source is controlled by the device per se which controls the actuator installed in the engine, based on an order signal of power supply of ON/OFF from the automobile driver, and is switched to OFF with certainty after the initializing operation is finished.
FIG. 5 shows construction of a conventional control device for an engine of an automobile. Explanation will be given to the operation of the conventional control device for an engine of an antomobile referring to FIG. 5. A reference numeral 1 designates a power supply switch, which is switched to ON/OFF by an antomobile driver. This ON/OFF signal is inputted to a power supply relay control circuit 35 in an engine control unit (hereinafter, ECU) 100 for an automobile, and a central processing unit (hereinafter, CPU) 32.
When the power supply relay control circuit 35 receives the ON signal, by outputting the ON signal to the base of a transistor Trl, the transistor Trl is switched to ON and an exciting current is flown in a coil 2a of a power supply relay 2 from a power source VB, a terminal 2b is closed, and power VB is supplied to a power supply circuit 31 in the ECU 100 through the terminal 2b.
When power is supplied to the ECU 100, the CPU 32 starts operating, and outputs a watchdog signal "a" to a watchdog detecting circuit 33. This watchdog detecting circuit outputs a reset signal "b" to the CPU 32, in case that the watchdog signal "a" is not inputted when an operational malfunction is generated in the CPU 32, or the like, restarts the CPU 32, outputs a load driving prohibiting signal to an actuator driving circuit 34, prohibits an output of a load driving signal "d" from the actuator driving circuit 34, and separates a load control from the CPU 32.
FIGS. 6A through 6E are timing charts for showing the operation of the conventional control device for an engine of an automobile. Simultaneously with when the power switch 1 is switched to ON, as shown in FIG. 6A, the power is switched to ON, as shown in FIG. 6E, the CPU 32 is operated, the watchdog signal "a" is outputted as shown in FIG. 6B, and a load driving allowing signal "c" is outputted from the watchdog detecting circuit 33 to the actuator driving circuit 34, the load driving signal "d" is outputted from the actuator driving circuit 34, as shown in FIG. 6D, and the driving of the actuator (load) is performed in the period of t.sub.NORM as shown in FIG. 6D.
Next, explanation will be given to the operation of the control device when the power is OFF, referring to FIGS. 5 and 6A through 6E. When the power switch 1 is switched to OFF by the driver of the automobile, as shown in FIG. 6A, the CPU 32 stops the normal control of the actuator (load), and starts the initializing operation. At the same time, the power supply relay control circuit 35, after receiving the OFF signal of the power switch 1, outputs the OFF signal to the transistor Trl after a predetermined time period of t.sub.1, demagnetizes the coil 2a of the power supply relay 2, and switches the terminal 2b to OFF.
Furthermore, when the watchdog signal "a" is not inputted from the CPU 32 to the watchdog detecting circuit 33, the reset signal "b" is outputted from the watchdog detecting circuit 33 to the CPU 32 as shown in FIG. 6C.
Since the conventional control device for an engine of an automobile is constructed as above, the initializing operation of the actuator requires at least time for the actuator to move to the reference position. The initializing operation may require several seconds, depending on where the actuator position is instantly before the initializing operation. As shown in FIGS. 6A through 6E, the delay time for making the power supply OFF of t.sub.1 is necessary to be longer than an initializing time t.sub.INI. There are two problems in the conventional device to achieve this with certainty.
(1) To realize a timer of several seconds or more in a circuit (t.sub.INI .ltoreq.t.sub.DMIN is satisfied in FIG. 6E), a condenser having a considerably large capacity is necessitated, which enlarges the scale of the ECU 100.
(2) Since the initializing control of the actuator is performed by the CPU 32, the initializing time t.sub.INI can accurately be controlled. However, the delay time for POWER OFF, t.sub.1 constructed by a circuit should be set to a large value having a considerable allowance with respect to a maximum value of t.sub.INI, considering age deterioration or the like of electronic components which constitute the circuit. As a result, current may be flown during a period of more than necessary after the driver switches off the power supply.